This invention relates to power units including an opposed piston internal combustion engine. It has application for example in engine driven reciprocating fluid compressors.
Most prior engine driven reciprocating air compressors comprise an engine coupled to an air compressor in which the power from the engine cylinder is transmitted to the compressor cylinder by means of the pistons, connecting rods, and crank shaft of the engine, the coupling between the engine and the compressor, and the crank shaft, connecting rods and pistons of the compressor. All these parts transmit the full power output of the engine and, with their associated bearings and running gear represent considerable weight and space.
Free-piston engine compressors are also known in which an opposed pair of engine pistons are directly and rigidly connected to respective compressor pistons and in which the stroke is variable. These, however, require special control devices which add to weight and complexity, in order, for example, to prevent excessive stroke when delivering against low pressure or excessive compression pressure in the engine cylinder when delivering against high pressure. In addition there is no carry-over of energy from one cycle to the next and, in consequence, they can be difficult to start and will stop instantly if combustion in the engine cylinder is not correct. Further disadvantages of the free-piston engine compressors are that the designer has inadequate control over speed since this is determined by the mass of the moving parts and the resultant of the pressures acting on them; and the absence of rotary motion which makes it difficult to drive cooling fans, water and oil pumps, and which necessitates unconventional and often heavy starting devices.